The invention relates to an apparatus and method for determining the location of a surface of, and more particularly the height of the top surface of unsingulated and possibly overlapping objects.
Automatic singulation, or separation into single items, of odd-shaped parcels, packages, letters, magazines or the like, herein designated mail pieces from a stack of such mail pieces, has been a problem for postal or mail courier services. Postal services and couriers are desirous of, and are at present in the process of converting from manual sorting of mail pieces to mechanized singulation. The problem of mechanical singulation is exacerbated by the odd shapes of many mail pieces, and by the tendency of mail pieces to overlap one another when dumped onto a conveyor.
Some mechanical singulation arrangements rely upon articulated robot arms terminated in end effectors or grippers adapted to pick up one mail piece at a time. Such robot arms may be controlled by a system which determines the location of the package to be picked up. U.S. Pat. No. 4,634,328 issued Jan. 6, 1987 in the name of Carrell describes a singulation system using cameras to determine the profile of the top piece in a pile of unsingulated mail for singulation thereof. U.S. Pat. No. 4,063,820 issued Dec. 20, 1977 in the name of Borgese describes an arrangement for using beams of light directed angularly relative to the surface of an object having a dimension to be measured. In Borgese's scheme, the object sits on a conveyor belt moving at known speed, so that the time lapse between the passage of the object through the beam provides information relating to its dimensions. U.S. Pat. No. 4,803,371 issued Feb. 7, 1989 in the name of Durland describes a system for determining size by the simultaneous use of non-coherent and laser light.
In systems for determining the size of an object in which a laser beam illuminates the object and in which a camera views the illuminated object, the optical limitations of the laser light projector and of the camera optical system cause the light beam as it is imaged onto the photosensitive surface of a camera to be diffused or spread out, possibly over several pixels. The spreading of the image of the laser beam introduces an uncertainty in the exact dimension and location of the mail piece. This inaccuracy, in turn, when translated into commands of a robot arm, may cause the robot arm to grasp the wrong mail piece, or to grasp a mail piece having actual dimensions larger than the measured dimensions in such a manner that the mail piece is damaged by the robot arm. Thus, a method for using one or more laser beams to accurately determine the dimensions, location, or both of a mail piece is desirable.